THE INTESTINAL CANAL. 1013 



the transverse and ascending portions and duodeno-jejimal angle, displace the 

 intestines in two ways. Seize the lower end of the omentum and turn it and the 

 transverse colon up over the chest-wall : then push the coils of the small intestine 

 below and to the left. There is now uncovered a large peritoneal surface formed 

 above by the lower layer of the transverse mesocolon, on the right by a layer of 

 peritoneum to cover the ascending colon, on the left by the right layer of the 

 mesentery, and below by the ileo-caecal angle. Shining through this common 

 layer one usually perceives a part of the duodenum, its inferior angle or trans- 

 verse portion. 



Sometimes none of it can be seen here ; that means a low duodenum, and in 

 order to disclose it, turn all the small intestines upward and to the right (Fig. 

 613). Then one sees perhaps a portion of the descending part, the pre-aortic 

 part, and always the ascending part, and duodeno-jejunal angle, escaping from 

 the mesocolon. * It has been noticed that when the transverse colon is held verti- 

 cally up above the body (the subject being supine) the transverse mesocolon forms 

 a horizontal partition. It divides the peritoneal cavity into two chambers a 

 superior gastro-spleno-hepatic, and an inferior intestinal. The ceiling of the 

 upper chamber is formed by the diaphragm, the sides by the inner surface of 

 the short ribs, and the floor by the upper layer of the transverse mesocolon. 

 The liver, spleen, and stomach form its contents. The inferior chamber is 

 limited above by the lower layer of the transverse mesocolon, on the sides by 

 the ascending and descending colons, below by the iliac fossse, while the middle 

 of this floor has been broken open to allow free communication between abdomen 

 and pelvis. This chamber contains small intestines. The duodenum makes a 

 bas-relief on the posterior walls of these two stories. The superior angle and a 

 part of the descending portion is in the upper one ; the rest of the descending 

 portion, all the pre-aortic and ascending portion, and often the duodeno-jejunal 

 angle, belong to the inferior story. Sometimes the duodeno-jejunal angle is in 

 the thickness of the mesocolon forming the partition. 



To describe the duodenal peritoneum of the lower chamber, reverse the great 

 omentum as before, isolate the mesentery and hold it tense, then follow the course 

 of its two layers. The left layer at first covers the part of the duodenum situated 

 to the left of this mesentery and then proceeds to lose itself below in the right 

 leaf of the sigmoid mesocolon, passing over the inferior mesenteric vessels ; to 

 the left it is continuous with the left prerenal peritoneum and right layer of peri- 

 toneum covering the descending colon ; farther above, this layer passes over the 

 left surface of the duodeno-jejunal angle and is continued into the inferior layer 

 of the transverse mesocolon. The right leaf of the mesentery covers the duode- 

 num to the right of this root and continues to cover the ascending colon ; below 

 it covers the ileo-csecal angle. Above, it passes upon the inferior layer of the 

 transverse mesocolon and on the right surface of the duodeno-jejunal angle. 

 Sometimes the two leaves of the mesentery embrace the duodeno-jejunal angle, 

 and, instead of immediately reuniting beyond, they leave a space between, form- 

 ing the orifice of the duodeno-jejunal fossa. The duodenum is crossed by two 

 mesenteries, the second portion by the transverse mesocolon, and the third or 

 fourth portion by the root of the mesentery. 



The first part of the duodenum is almost completely covered by peritoneum 

 derived from the two layers of the lesser omentum. Only a part of its posterior 

 surface near the vena cava and neck of the gall-bladder is uncovered. The supra- 

 colic part of the descending portion has no posterior covering. Its right and 

 anterior surface are covered by peritoneum from the anterior surface of the right 

 kidney : its left side is covered by peritoneum of the lesser sac. Next on its 

 anterior surface is a non-serous region corresponding to the interspace between 

 the layers of the transverse mesocolon. The infracolic part of the second portion 

 is covered by the right leaf of the mesentery. 



A part of the pre-aortic portion has only an anterior covering from the right 

 leaf of the mesentery. Depending on the position of the radix mesenterii and 



